to borrow a few passages from the documentation packaged with john walker's demoronizer.pl:

...as is usually the case when you encounter something shoddy in the vicinity of a computer, Microsoft incompetence and gratuitous incompatibility were to blame. Western language HTML documents are written in the ISO 8859-1 Latin-1 character set, with a specified set of escapes for special characters. Blithely ignoring this prescription, as usual, Microsoft use their own "extension" to Latin-1, in which a variety of characters which do not appear in Latin-1 are inserted in the range 0x82 through 0x95--this having the merit of being incompatible with both Latin-1 and Unicode, which reserve this region for additional control characters.

These characters include open and close single and double quotes, em and en dashes, an ellipsis and a variety of other things you've been dying for, such as a capital Y umlaut and a florin symbol. Well, okay, you say, if Microsoft want to have their own little incompatible character set, why not? Because it doesn't stop there--in their inimitable fashion (who would want to?)--they aggressively pollute the Web pages of unknowing and innocent victims worldwide with these characters, with the result that the owners of these pages look like semi-literate morons when their pages are viewed on non-Microsoft platforms (or on Microsoft platforms, for that matter, if the user has selected as the browser's font one of the many TrueType fonts which do not include the incompatible Microsoft characters).

You see, "state of the art" Microsoft Office applications sport a nifty feature called "smart quotes." (Rule of thumb--every time Microsoft use the word "smart," be on the lookout for something dumb). This feature is on by default in both Word and PowerPoint, and can be disabled only by finding the little box buried among the dozens of bewildering option panels these products contain. If enabled, and you type the string,

"Halt," he cried, "this is the police!"

"smart quotes" transforms the ASCII quote characters automatically into the incompatible Microsoft opening and closing quotes. ASCII single and double quotes are similarly transformed (even though ASCII already contains apostrophe and single open quote characters), and double hyphens are replaced by the incompatible em dash symbol. What other horrors occur, I know not. If the user notices this happening at all, their reaction might be "Thank you Billy-boy--that looks ever so much nicer," not knowing they've been set up to look like a moron to folks all over the world.

these characters are commonly inserted into form elements via cut and paste operations. in many cases, they are converted to UTF-8 by the browser. this plugin will replace both the unicode characters AND the Windows-1252 characters with sane ASCII equivalents.